Opening devices of different types provided on a packaging container formed by packaging sheet material and adapted for containing substances such as foodstuffs, and in particular for containing liquid beverages such as juices, water, milk, wine, etc. are known.
One such opening device includes a perforation on a wall part of the packaging container and a plastics material lid device attached to the wall part and covering the perforation in a closed state. The lid device includes a circumferential base attached to the wall part, for example by means of adhesives, circumferentially surrounding the perforation, and a lid element hinged to the base. Once the lid element is opened, the perforation may be engaged and forced open so that the contents inside the packaging container may be dispensed therefrom.
Another known opening device includes an opening provided on a wall part of the packaging container and a plastics material lid device similar to the one described above attached to the wall part and covering the opening in a closed state. A sealing element such as an aluminium pull tab is connected to the wall part so as to cover the opening, and once the lid element has been opened, the sealing element may be removed to expose the opening for dispensing the contents of the packaging container.
Methods for providing the above opening devices on the packaging containers may include feeding a continuous web of packaging material to a first station at which the perforation or opening is provided on the web, and to a second station at which the lid element is attached to the web for covering the perforation or opening. The aluminium pull tab, if provided i.e. for covering the opening, is attached in an intermediate step. After the opening devices are provided on the web, packaging containers from the web are formed, filled with product, and sealed, such that the opening devices are arranged on the finished container packagings for easy access.
One example of a machine for forming, filling, and sealing packaging containers is the TB8 filling machine, manufactured by Tetra Brik Packaging Systems of Modena, Italy.
As an alternative to the above opening devices, in which an already formed plastics material lid device is applied to the sheet, U.S. Pat. No. 4,725,213 (the disclosure of which is incorporated herein by reference) discloses a plastics material opening device which is injection moulded directly onto the sheet of packaging material. In particular, a pair of mould tools are moved into arrangement about a prestamped hole in the sheet, and heated thermoplastics material is injected through an injection passage defined between one of the mould tools and one surface of the sheet and extending along such surface of the sheet in order to form the opening device at the prestamped hole.
Although the method and apparatus for providing this latter type of opening device may be completely valid, there exists in the field of thermoplastics material injected opening devices the need for further improvements.
The injection passage in U.S. Pat. No. 4,725,213 extends from the injector head for a significant distance along one surface of the sheet to one end of the mould cavity for forming the opening device, so as to create a number of disadvantageous effects. Since the injection passage enters the mould cavity at one end, the complete filling of the mould cavity with heated thermoplastics material is rendered difficult and inefficient particularly at the portion of the mould cavity arranged distally from the injection passage. Moreover, if the injection passage extending along one surface of the sheet is excessively long, the filling of the mould cavity is rendered even more difficult and inefficient, and therefore the apparatus and method are limited to moulding opening devices arranged substantially only near the edge of the sheet at which the injection head is positioned. Additionally, a strip of plastics material is formed in the injection passage, and further steps must be made to eliminate such strip, which is additionally inefficient and which creates the possibility of damaging the opening device from which such strip must be removed. Further complications arise from subjecting the surface of the sheet of packaging material, which generally has a very low stiffness and resistance, to thermoplastics material at elevated pressures and temperatures injected into the injection passage.
The above described difficulties in completely filling the mould cavity may lead to a situation in which plastics material will not flow to all parts of the mould cavity and as a result, the edge of the opening may not be sufficiently sealed by plastics material of the opening device. Generally, the packaging sheet material is formed of several layers including an inner paper layer and two outer synthetic plastics material coating layers, one of which is destined to form a product contact surface. Other possible layers such as printing ink layers, laminating layers and aluminium foil layers may be interposed between the paper layer and the outer coating layers. When the opening in the packaging sheet material is stamped, the internal layers of the packaging sheet are exposed at the edge of the opening, and unless such edge is adequately sealed by the injected thermoplastics material opening device, the packaged product may come into contact with the internal layers of the packaging sheet material possibly causing damage thereto. Moreover, the overall efficiency of the apparatus and method is compromised when the time needed to inject the heated thermoplastics material for each mould operation is increased so as to assure an adequate filling of the mould cavity.
The mould tools in U.S. Pat. No. 4,725,213 consist of a pair of mould tools which are both movable in opening and closing directions which extend perpendicularly to the extension of the sheet. Such a configuration substantially limits the flexibility of the device in forming opening devices with different shapes, since the mould tools must not encounter any portions of the opening device which protrude in a direction perpendicular to the direction of movement of the mould tools. The injection moulded opening device of U.S. Pat. No. 4,725,213 indeed includes a pull tab which extends in a direction perpendicular to the sheet, for a long extension sufficient to be gripped by a user. Such an extensively protruding pull tab is disadvantageous with regard to storing and shipping packaging containers including an opening device of this type.
It is furthermore desirous to have opening devices with base portions connected to the sheet hole and lid portions positioned in planes which are slightly raised with respect to the base portions and the packaging sheet. These lid portions have an edge or lip which extends parallel to the extension of the packaging sheet, so that they may be gripped and opened by a user. The apparatus of U.S. Pat. No. 4,725,213 is incapable of forming opening devices of this type due to the opening movement of the mould tools.
What is needed is an apparatus and method for injection moulding a thermoplastics material opening device onto a packaging material sheet which allows to assure that the opening device is moulded in a most effective and efficient manner possible.